Optical coherence tomographic imaging methods and apparatus have been finding practical applications in recent years, applying techniques of low coherence interferometry and/or white light interferometry. In particular, optical tomographic imaging apparatus (optical interferometric measurement apparatus) for optical coherence tomography that utilizes multiwavelength optical interferometry can obtain cross-sectional images of samples with a high resolution so that such apparatus are becoming indispensable for obtaining tomographic images of fundi and retinas in the field of ophthalmology. Besides ophthalmology, dermatological cross-sectional observations and cross-sectional imaging of walls of digestive organs and circulatory organs, using endoscopes and catheters are under way. Optical coherence tomography will be referred to as OCT hereinafter in this specification.
Since OCT utilizes properties of light, an object can be measured with a high resolution of micrometers, or of the order of the wavelength of light, by means of OCT. However, while OCT allows fine measurements, a long measuring time is required to measure a wide region. Particularly, when the object of measurement is a part of a living body such as a human eye or the wall of a digestive organ that moves finely and randomly, the image obtained as a result of measurement can be distorted unless the measurement is conducted faster than the speed of the fine motion. Additionally, three-dimensional data need to be obtained from the object of measurement and an image of an arbitrarily selected cross section of the object needs to be synthesized for observation from the obtained data in order to examine the object more accurately. Then, the object needs to be measured very quickly.
In recent years, there is a rapid advancement in the technology of Fourier domain OCT apparatus that can obtain data in the direction of optical axis collectively if compared with time domain OCT apparatus. The Fourier domain OCT allows acquisition of data of a line in the direction of optical axis to be measured in cycles equal to tens of several kHz, which represents a speed of measurement that is several hundreds times of the speed of measurement of the conventional time domain OCT. For example, while the time domain OCT takes a second to obtain a cross-sectional image formed by 1,000×1,000 pixels by scanning a measurement light for a line in cycles equal to 500 Hz, the Fourier domain OCT takes only about 0.05 seconds because the Fourier domain OCT scans at a line measuring rate of 20 kHz.
With another high-speed measurement method, a broad region is divided into a plurality of sub-regions, which are then measured simultaneously by means of the same number of measurement lights. Japanese Patent No. 2875181 discloses an optical tomographic imaging apparatus that employs a plurality of light sources and the same number of photosensors and the individual photosensors are made to operate for the respective light sources by means of a common focusing optical system.